1. Field of the Invention
The present invention relates to zoom lenses having a zooming function and optical instruments having the zoom lens.
2. Description of the Related Art
Extremely strict specifications especially in a color shift (lateral chromatic aberration) among optical functions are required for zoom lenses used in liquid crystal projectors in response to the demand for higher fineness of projected images.
In general, for correcting the lateral chromatic aberration, it is effective to use a lens made of anomalous dispersion glass.
For example, one conventional system discusses the use of a zoom lens that is corrected in lateral chromatic aberration using a lens made of the anomalous dispersion glass, where the zoom lens is used in a liquid crystal projector (U.S. Pat. Nos. 6,816,320, 7,016,118).
Recently, the market has emphasized a strong demand for a zoom lens, for use in a liquid crystal projector that has a higher zoom ratio, a wider angular field, and a larger aperture for using illumination light at higher efficiency, as well as a higher optical performance over the entire zooming region. These demanded characteristics widely relate to the correction of various aberrations including spherical aberration and lateral chromatic aberration and changes in aberrations accompanied by zooming.
In particular, the changes in spherical aberration and lateral chromatic aberration involved in zooming greatly affect the optical performance among the demanded characteristics, so that the reduction thereof has been required.
In order to have high optical performance while favorably correcting the spherical aberration and the lateral chromatic aberration over the entire zooming range, the lens configuration and the material of each lens must be appropriately established.